Proximal isovelocity surface area (PISA) in the evaluation of fixed membranous subaortic stenosis.

The evaluation of the severity of subaortic stenosis is usually expressed by the magnitude of the subvalvular gradient. Calculation of the membrane orifice area noninvasively is difficult by the standard means. We present a patient in whom the area was calculated using the proximal isovelocity surface area (PISA) method. This method should have clinical applicability because it is not flow dependent and can be used in patients with normal, reduced, or increased stroke volume.